Windchill is for wimps -- it's the ultimate weather statistic of the Age of Feelings, a trick that adds drama and bragging rights to people's lives while it debases the currency of true cold weather.
"Boy, it was cold yesterday," you say. "My porch thermometer showed 9 degrees when I got up."
But somebody always trumps your ace.
"It was 20 below at our place," they say. "With windchill."
As Virginia State Climatologist Patrick Michaels puts it: "Windchill is a way of saying 'Mine is bigger than yours.' It's the 'I'm suffering more than you're suffering' index. It came into popular usage in the mid-1960s thanks to newspaper people. Imagine two newspapers -- one says it's minus 5 degrees and the other says that it's minus 55 with windchill. Which one do you buy?"
And what temperature is it, actually?
In International Falls, Minn., which bills itself as the Nation's Icebox, Chamber of Commerce Director Evelyn Henrickson was bragging yesterday that it was 45 below zero, windchill, and it had been 65 below zero on Monday. The difference, she said, was that on Monday "my car started."
Wait a second. Wasn't it colder on Monday?
No. It was warmer. "It was 19 below, and today it's 26 below," she said. "Without windchill."
The problem is that cars don't pay any attention to windchill, once they get down to what the thermometer says the temperature is -- and International Falls is building a 22-foot-tall thermometer to do just that, and prove that it's them, and not Fraser, Colo., that deserves the title of "Nation's Icebox," though that argument has nothing to do with windchill.
As it happens, the windchill factor is a number that doesn't tell you anything about how cold it is, but only about how fast you get however cold it is.
"It's a rate phenomenon," says Murray Hamlet, a veterinarian who directs the cold research division of the Army Research Institute of Environmental Medicine. "It's a derived formula that comes from the research of a man named Paul Siple in Antarctica in 1940. Siple wanted to describe the cooling power of wind on exposed flesh, the ability to remove heat from that surface."
Siple set plastic containers of water out in freezing cold, and noticed what any sled dog could have told him, which is that they froze faster when the wind blew. In 1945, Siple and Charles F. Passel published their findings in a journal of the American Philosophical Society. Strangely enough, an experiment this simple has generated debate ever since. For instance, Siple hypothesized that above about 40 or 50 miles an hour, it doesn't matter how hard the wind blows, you won't get any colder any faster.
"A slight skepticism concerning Siple's findings is warranted," says Greg Gordon, a weather observer for 10 years on the top of Mount Washington, in New Hampshire. "About two or three times a week, on and off for a few years, I've been going up on the top of a tower here and exposing my hand to the wind. I try to be at rest and comfortably dressed. I hold my hand up until the outer layer of skin freezes -- it turns the skin white and makes a welt. When that happens, I put it back in my mitten. Today it's 14 below zero with the wind blowing 70 miles an hour and it'll probably take about 25 seconds. I can tell you that there's an appreciable difference between 50 miles an hour and 70 miles an hour. It's common sense."
What happens, up there on the tower, is that the wind blows away what's known as the "boundary layer" of heat that eddies for a millimeter or two above Gordon's skin. The faster this boundary layer gets ripped away, the faster the skin cools.
Unfortunately, windchill tables put out by the National Weather Service follow Siple's rule and don't provide figures for wind speeds above 45, but like anyone else caught out in the cold, Gordon can discover the rate at which he is losing heat, according to one published formula, simply by multiplying the wind speed in meters per second by 100, taking the square root and adding 10.45, subtracting the wind speed and multiplying by 33 minus the air temperature in centigrade. (Isn't this an old Eskimo trick?)
The standard tables go up to either 35 or 39 degrees Fahrenheit, which is a little bit of a mystery, seeing that as long as the temperature is over freezing, no amount of wind will get it below freezing, not even on the top of Mount Washington. Then again, nothing ever gets as cold as windchill, either. Once Evelyn Henrickson's car engine got down to 26 below yesterday morning in International Falls, no amount of wind would make it colder. (Things weren't helped much, she said, by the fact that her "head bolt heater wasn't on.")
Also, when it gets cold enough, people stop caring about these differences. In the real world, as Virginia's Michaels says, "operational effect is minimal. It's like the difference between hailstones the size of grapefruit and hailstones the size of canned hams. There isn't much."
The question is, where does windchill stop, and humiture begin? Humiture is another one of these formula numbers, like the comfort index, that combines temperature and humidity, as opposed to temperature and wind speed, to tell you how the weather feels, rather than what it is.
"There's a no man's land between windchill and humiture," Michaels says. "We call it California."
At the National Weather Service, meteorologist Hank Robinson admits about windchill: "The numbers aren't firm. Windchill of 45.3 does not differ appreciably from 45.5."
Isn't this physics, though? Aren't we talking about the kind of basics any American schoolchild can understand?
"We are not dealing with all the parameters," Robinson says.
The parameters, when you're talking about people and not plastic containers of antarctic water, include things like clothing, metabolic rate, body fat, age and the fact that the rules are different for warmblooded animals and coldblooded ones -- a lizard takes the cold about as badly as Siple's containers of water.
This doesn't even begin to get into the ancient debate between wet cold and dry cold.
"Humidity has a minor effect," says Michaels, pointing out that even when cold air has 100 percent humidity, it has less water per cubic foot than warm air at 100 percent humidity.
"The cooling power is more," counters Mount Washington's Gordon, pointing out that when you're hot, and you pour water on yourself and turn on the fan, you get cooler faster than you would if you were dry.
Of course, on top of Mount Washington, it would seem that moisture would play a small role, seeing that there doesn't seem be a lot of evaporation when it's minus-14 outside and you're watching your hand turn into a white welt.
"Are you kidding?" Gordon says. "Water will evaporate down to 200 below. There's no liquid transaction, but it evaporates. But this gets into that business about whether it's evaporation, sublimation or efflorescence, and I'm not going to get near that one." Gordon also denies that a hot wind makes you hotter if the air temperature is over body temperature. "Unless, of course, it gets up to about Mach 3, and the friction of the wind heats you up," he says.
The Army's Hamlet disagrees, citing the example of Arabs protecting themselves from hot wind with layers of wool robes. But this is a whole 'nother argument. What's more important in weather like we've been having lately is the fact that he agrees that wet cold air cools you faster than dry cold air. "The more water, the more it will conduct heat."
Where the windchill factor has value, Hamlet says, is in "threat analysis."
If you're dressing your children for school, going for a hike in the snow or calculating the hazards for street people, it tells you how fast people are going to get cold, and how much clothing they should wear to slow that process down.
"It's only a red flag as far as we're concerned," says the National Weather Service's Robinson, adding that it's not entirely necessary for the future of mankind. "I think folks back in the Middle Ages knew about it. When it's cold and the wind is blowing, it's time to wrap up."
As for hard science, bragging rights and starting your car, stick with an old-fashioned thermometer.